In the packaging of many items, such as bagged cereal and bottled beer, the items are inserted into cartons from a generally horizontal direction. That is, the items are side loaded, rather than top loaded. Side loading is a more efficient and reliable assembly line method for certain products.
After loading of the product, the opposed ends of the cartons are sealed. An exemplary sealing process includes four adhesive applicators. First and second applicators are aligned on opposite sides of the assembly line and each directs a flow of adhesive onto minor flaps which have been folded to be perpendicular to the carton sides. The first and second applicators function identically to provide the first step in sealing the opposed ends of a carton. A carton then moves downstream of the two applicators and a hinged major flap on each end of the carton is folded to contact the adhesive on the minor flaps. Setting of the adhesive seals the flaps. Further downstream third and fourth adhesive applicators provide a second deposition of adhesive on the minor flaps, whereafter another major flap is folded to contact the second deposition. Typically, each of the four applicators includes two heads. One head deposits adhesive on a forward minor flap, while the other head deposits adhesive on the rearward minor flap. The carton is oriented so that the length of the minor flaps extend in a vertical direction. A hinged major flap that is folded downstream of an applicator has its length parallel to the direction of carton movement.
There are a number of difficulties involved in the above-described automated assembly line process. Adhesive is projected from the applicator heads onto the surfaces of the carton. The velocity of the adhesive must be sufficiently high to insure a reliable positioning of the material on the carton surfaces to minimize adhesive usage. This requires use of relatively small orifices in the outlet nozzles of the applicators. Nozzle orifices in the range of 0.012 to 0.014 inch are common. Moreover, high adhesive pressures of 600 to 700 psi are used. The projection of adhesive over an extended distance from small-orifice, high-pressure applicators causes stringing between adhesive applications. Stringing occurs at the tail end of an application, as the viscosity of the adhesive provides a tendency of released material to urge remaining material from the nozzle orifice. The material strings across the product, the carton and the moving parts of the assembly line. Consequently, the assembly line must be periodically shut down to allow cleaning and preventive maintenance.
The small orifice nozzles have a tendency to plug at an unacceptable rate. This is particularly true in use with hot-melt adhesive, since adhesive material that has been charred will plug a small diameter orifice. Often a nozzle of an applicator head will include more than one orifice. When a portion of the orifices are plugged, the applicator head will continue to seal cartons but the seal will be a marginal one. This leads to a serious quality assurance problem and to damage of the product should the seal give way to the weight of the product.
As described above, the cartons receive a deposit of adhesive and then move downstream of the adhesive application site for closing of a flap. An assembly line problem which is encountered involves the setting of hot-melt adhesive at the application site when the assembly line is stopped for adjustments, modifications or emergencies. If the assembly line cycle stop lasts for a substantial period of time, the adhesive will have set before the major flap is folded into contact with the adhesive. Thus, cartons which are located at application sites during a cycle stop will have a major flap that is free to pivot to an open position. Those cartons must be located and either discarded or individually treated to provide the required seal. Some assembly lines include a cycle-stop flap closing mechanism at each application site. These mechanisms may be pneumatically controlled closure bars which are actuated only upon stoppage of carton travel. The pneumatic bars pivot the major flaps and press the flaps against the surfaces on which adhesive has been deposited. In this manner, setting of the adhesive at the application sites does not result in a defective sealing of a carton. However, pivoting of the major flap will cause contact of the flap with the applicator unless the applicator is spaced apart from the carton by a sufficient distance. At a minimum, the distance must be 1.5 inches. Therefore, the assembly line will be susceptible to the stringing, nozzle plugging, and quality assurance problem described above. Additional problems involve excess material usage and a safety hazard inherent with high pressure adhesive application.
It is an object of the present invention to provide a system for use on an automated assembly line which is clean, safe, cost-efficient and reliable and which insures that all cartons on the assembly line are efficiently sealed despite periodic unanticipated stoppage of assembly line operation.